Motor vehicles with a hybrid drive (hereinafter referred to as hybrid vehicles for short) that comprise both an internal combustion engine and an electric drive are known from the prior art.
In this case it is possible for only the electric drive to be connected to the wheels of the motor vehicle, the internal combustion engine being used, by way of a generator, to power the electric drive or an electric battery, which constitutes an energy source for the electric drive.
In other hybrid drive designs both the internal combustion engine and two electric drives transfer their drive energy to the vehicle wheels via a common gear arrangement, the arrangement also comprising a generator that is used to generate electric energy during operation of the internal combustion engine.
In another hybrid drive design, as is shown schematically in FIG. 1 with reference to a hybrid drive arrangement 1, an internal combustion engine 5 having a drive shaft 6 and an electric drive 3 having a drive shaft 4 act on a common crankshaft 10 in such a way that the torques of the internal combustion engine 5 and of the electric drive 3 are added together. A conventional gear unit 15 adapts the torques of the internal combustion engine 5 and of the electric drive 3 to the respective driving conditions.
A coupling 20 is arranged between the internal combustion engine 5 and the electric drive 3 in such a way that the electric drive 3 can be operated independently of the internal combustion engine 5 so as to drive one or more driving wheels 25 via a gear unit 15, drive train 30 and differential gearing 35.
The internal combustion engine 5 is conventionally started by a starter motor or belt starter generator 40, the belt starter generator 40 being connected to the crankshaft 10 via a belt pulley 42 and a belt 44.
At least a control unit 50 controls the internal combustion engine 5, the belt starter generator 40, the electric drive 3 and the gear unit 15 via corresponding control commands.
An electric energy source 55 supplies the belt starter generator 40 and the electric drive 3, which can also be operated as a generator, with electric energy, the electric energy source 55 also being able to store electric energy supplied from the electric drive 3 if the electric drive 3 is operated as a generator driven by the internal combustion engine 5.
The hybrid drive design shown in FIG. 1 only allows the vehicle to be driven by the drive power of the electric drive 3 when the internal combustion engine 5 is not in operation. The electric energy required to operate the electric drive 3 is supplied by the energy source 55. Operating states of the internal combustion engine 5 with low load, which would lead to poor efficiency of the internal combustion engine 5, can thus be avoided. A purely electric drive is particularly advantageous in urban traffic, where it is often only possible to drive with low load, since fuel can thus be saved and the emission of pollutants is reduced.
If the electric energy source 55 can no longer provide sufficient energy, i.e. if, for example, a specific voltage threshold value at which the electric drive 3 would no longer function is not reached, or of the driver requires greater torque, the internal combustion engine 5 is connected via the coupling 20.
If a situation occurs in which it is required to operate the internal combustion engine 5 in addition to the electric drive 3, the drive train and therefore the electric drive 3 and the (just started) internal combustion engine 5 are generally arranged at different speed levels. The internal combustion engine 5 may thus have a standard idling speed of approximately 700 to 1400 revolutions/minute, whilst the drive train and the electric drive have a speed of approximately 2000 to 5000 revolutions/minute. If the coupling 20 is closed in a situation of this type, the drive train will jerk, which is detrimental for driving comfort and may also be damaging for the components of the drive train.